2009-06-23

Making Connections the IDC Way

One of the most annoying parts of prototyping can be connecting everything up. With the solderless breadboard, everyone starts off with "ye bundle of telephone wire" and gets pretty adept at stripping back the ends and board stuffing. After a few uses, the ends bend up and soon thereafter get tossed in the wastebasket.

One of the nicer pieces of equipment for wire-up are the male header pin cables currently available for use with 0.100 spaced boards. These give you a flexible wire with a solid header pin just made for board insertion and fit well side by side on the board.

That's all well and good for two or three wires side by side, but what if you want to run a three wire cable over to a sensor three feet away, or want to jump eight digital ports from an Arduino 2009 over to a solderless board because you haven't quite yet committed to stuffing one of those really nice proto-shields full of components for a potentially flaky circuit?

You could get some ribbon cable, strip back the ends, get out the needle-nose pliers and solder them down to some header pins. That works for a while, but if you aren't careful, somewhere along the way, one of the wires breaks after too many flexures, plus there isn't much room for getting a grip on the header to pull it out. The other method is to use crimp female header sockets, but then we're back to stripping wire and I've had to deal with rotten, cheap crimpers that almost but not quite crimp about one in every four sockets. Enter a connection method used in the avionics industry...

This is known as an IDC (Insulation Displacement Connector). This particular version is made for 0.100" single row headers and 22 gauge wire. It's a little overkill for our purposes. The ribbon cable we're working with is typically 28 gauge. Let's have a look at the Amp MTA 100 series IDC.

Here we have a 3 pin connector. The wires slide into the top of the connector with the ends flush against the vertical wall at the back of the connector. For production purposes, this female connector has a mating male connector that solders into the board. It has a clip locking action, but that is superfluous for prototyping.

The wires are inserted into the connector with a punchdown tool.And visually, here's the process: 1) Cut the ribbon cable to length. 2) Separate the wires. 3) Insert first wire with end touching wall. 4) Punch down with tool.

And here's the finished connector and a finished 18" 3-wire cable for about $1.40. Female/female servo style cables are readily available for about $3.00, but where this shines is when you want four or more wires in your cable.

The final bit for making this work with your solderless breadboard is to get out your snappable double-side header pins, snap off the appropriate number, push the long end into the socket and you have an instant male/male cable that will insert into the Arduino socket and your solderless breadboard.